How far is the spiral nebula?

Both shapley and Curtis know very well that the key to resolving the dispute is to estimate the distance of the vortex nebula.

19 17 astronomer Ricky, who works at Mount Wilson Observatory in the United States, accidentally discovered a nova explosion in NGC6946 nebula. As a result, the negatives of other nebulae observed on Mount Wilson were also searched and more new stars were found.

Curtis of Rick Observatory is also involved in the search for new stars. He believes that the discovery of new stars proves that spiral nebulae are not disk-shaped gas clouds, but independent star systems outside the Milky Way.

He also put forward some other arguments. Curtis pointed out that the angle of each spiral nebula is very different. The angular size of the nearest Andromeda nebula is 2 degrees, while the angular size of some small spiral nebulae is only 10' or even smaller. If they are similar in size, then their distance from us will be obviously different. Assuming that the Andromeda Nebula is at the edge of the Milky Way, these small nebulae will be more than 10 times farther than the Andromeda Nebula. Therefore, it is unreasonable and impossible to include all spiral nebulae in the Milky Way. They should be independent galaxies outside the Milky Way.

1885, a new star named Andromeda was observed in the Andromeda nebula, and its brightness was equivalent to that of the Milky Way. Shapley could not have known that it was a supernova with much greater brightness than the nova at that time, but he thought it was very close. This became another reason why shapley opposed Curtis.